abs cannot be used in problem-based optimization expression

Can someone tell me why I cannot use abs() in this simple setup.

prob = optimproblem();
x = optimvar('x',1,1);
y = 1;
x0 = struct('x',0);
prob.Objective = abs(x-y); % sum(abs(x-y)) also doesn't work

Incorrect number or types of inputs or outputs for function 'abs'.

%prob.Objective = norm(x-y,1); % this however works

sol = solve(prob,x0)

If I use prob.Objective = norm(x-y,1) it wokks just fine

Answer 1

[Bruno Luong]

Nevermind abs is not supported function https://www.mathworks.com/help/optim/ug/supported-operations-on-optimization-variables-expressions.html

[Torsten]

sqrt((x-y).^2) doesn't seem to work, either.

[Bruno Luong]

Syntaxically it works, but I have to add a small margin to avoid singularity of the derivative at 0

prob = optimproblem();
x = optimvar('x',1,1);
y = 1;
x0 = struct('x',0);
prob.Objective = sqrt((x-y).^2+eps); % sum(abs(x-y)) also doesn't work
sol = solve(prob,x0)

Solving problem using fminunc.

Local minimum found.

Optimization completed because the size of the gradient is less than
the value of the optimality tolerance.

sol = struct with fields:
    x: 1